protactinium

(prō′tak tinē əm)

noun

a rare, radioactive, metallic chemical element, one of the actinides, found in pitchblende: symbol, Pa; at. no., 91

Origin: ModL: see proto- & actinium

See protactinium in American Heritage Dictionary 4

noun Symbol Pa
A rare, extremely toxic, radioactive element chemically similar to uranium, having 13 known isotopes, the most common of which is protactinium 231 with a half-life of 32,480 years. Atomic number 91; melting point 1,230°C; specific gravity 15.37; valence 4, 5. See Table at element.

Origin:

Origin: prot(o)-

Origin: + actinium (so called because it decays into actinium)

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